Mirroring to start Symmetry - object doesnt flip
There are a couple of ways to mirror an object in Blender:


Mirror Mofifier


This is an undestructive method to mirror your object with the most control. Go to the object's modifier panel and add a mirror modifier:

(Blender doc: https://docs.blender.org/manual/en/latest/modeling/modifiers/generate/mirror.html)




Edit Mode Mirror


Go into Edit Mode, and press 'CTRL+M' or in the menu go Mesh>Mirror>Desired Axis

This is a destructive but direct solution to mirror your object.

(Blender doc: https://docs.blender.org/manual/en/latest/modeling/meshes/editing/transform/mirror.html#mirror)